Mapping the CMU
Having your CMU (Content Mapping Unit) properly mapped to your targeted display is an essential part of your Dolby Vision work-flow. In particular, the external mapping unit, or eCMU, must be manually configured to achieve the desired results.
Common eCMU issues
This issue is typically caused by the lack of metadata or perhaps the incoming SDI signal from the color corrector. Firstly, make sure the SDI signal is present (Refer to eCMU status: “Waiting for input signal” for more details).
If the issue persists, then it is highly possible due to the metadata.
Make sure your eCMU has been connected to the color grading host via ethernet, and the IP address is correctly configured.
Make sure the valid Dolby Vision licenses have been installed successfully. There are two license files to be installed before the CMU will become active. (Refer to CMU user manual and License Key Upload Instructions for more details).
(The Licensing tab is a good clue to verify CMU license status.)
Analyze one shot on the timeline to ensure that there is valid metadata being generated and sent out from your color corrector.
In some certain versions of color corrector software, ( Resolve 14.xx, for example), CMU wouldn't start mapping until the L2 trims are modified. If this is your case, upgrading the software may help.
Is your CMU in 'pass-through' mode? If yes, switch to 'Normal' mode
Is your CMU working in HDMI tunneling mode? If yes, switch to SDI mode
Contact your CMU vender for more support if the above trouble shooting does not help.